Many general aviation aircraft have the capability to operate at altitudes which present issues with respect to oxygen saturation of both pilots and passengers. In the United States, the Federal Aviation Regulations require that flight crews use oxygen if operating above 12,500 feet mean sea level for more than 30 minutes and at all times if the aircraft is operating at or above 14,000 feet altitude. And, passengers must be offered oxygen in unpressurized aircraft operating above 15,000 feet altitude. As the operating altitude of an aircraft increases, the “time of useful consciousness” or “TUC”—the amount of time that a pilot is able to perform his or her flying duties properly in the absence of suitable oxygen supply—becomes increasingly shorter, and thus, is critical. For example, while the TUC may be 30 minutes or more at FL 150 (15,000 feet in altitude), when at FL 250 (25,000 feet in altitude), the TUC may be only 3 to 5 minutes, or less, especially if under stress (or, for example, if exercising). Moreover, in the case of pressurized aircraft, an incident of sudden decompression may significantly decrease the TUC.
Increasingly, high performance general aviation aircraft are available, from the factory, with turbocharged piston engines. Such aircraft are able to provide excellent performance, e.g., high speed, when operating in the low “flight levels”—from about 15,000 feet up to about 25,000 feet, or more. Since the middle of the 1960's, Cessna, Beechcraft, Piper, Mooney, and other manufacturers have produced thousands of piston engine powered aircraft equipped with turbochargers that are capable and certified for flight in the middle flight level altitude ranges (18,000 to 30,000 feet, or, by standard abbreviation, simply FL 180 to FL 300). In addition, there are multiple turbocharger systems that are approved by the FAA for retro-fit on general aviation aircraft to convert normally aspirated engines to turbocharged engines, and those aircraft have the same high altitude capability. Such conversions are commonly accomplished using a Supplemental Type Certificate (STC) issued by the FAA. As used herein, the terms “turbocharged” or “turbosupercharged” or variants thereof, includes within their scope the term “turbonormalized” as it may refer to aircraft engines whose turbochargers provide only for sufficient boost pressure to equal that provided by a normally aspirated engine operating at sea level.
In any event, operation of aircraft provided with such turbo systems puts pilots, and their passengers, at altitudes where, in those rare circumstances when a mechanical problem causes a fault or other interruption in the normal oxygen supply used by the pilot, the pilot must recognize the fault condition and then take prompt steps to either restore the oxygen supply or cause the aircraft to descend to lower altitudes, since the actual available time of useful consciousness may be quite limited.
Pilot incapacitation as a result of hypoxia, i.e. lack of adequate oxygen when operating at altitude, has been suspected as a possible cause of one or more accidents involving both jet powered and piston powered aircraft. In one case, a Lear Jet cabin pressurization system failed and resulted in a fatal accident after the aircraft flew an extended path across the United States with an unconscious crew. In another accident also involving a turbine powered aircraft, a Helios Airways Boeing 737 crashed in August 2005 into a mountainous area in Greece, after the crew evidently lost consciousness after failing to properly respond to various alarm systems. More recently, there has been an accident involving a popular general aviation turbo charged aircraft where the pilot became incapacitated and overflew the flight planned destination, while the aircraft continued on under command of a sophisticated autopilot at an altitude of 25,000 feet, until the aircraft ran out of fuel on the selected fuel tank. Such accidents, and others, point to the need for installation of aircraft flight control systems with the capability to take over, at least to some limited extent, control of an aircraft in the event the crew becomes incapacitated or otherwise unresponsive, for example, if due to reduced blood oxygen saturation. With respect to large turbine powered aircraft, the presence of auto-throttles and other automated flight control systems may provide opportunities to easily install further programming responsive to such need. For example, Airbus Industries has disclosed work on development of an “auto emergency descent” feature for integration with existing flight management systems. As reported, if flight crew members are disabled by hypoxia, the system would bring the aircraft down to 10,000 ft to help the pilots recover consciousness. Currently, the system is reportedly being developed for initial use on the Model A350XWB aircraft, where the system would initiate commands, in the absence of crew action during a warning period, to descend at a maximum operating speed to level off at 10,000 feet, or a minimum en-route altitude. On the other hand, with respect to piston engine powered general aviation aircraft, autopilots are generally provided for “two-axis” operation—that is, up/down and left/right directional control—but the engine operation is largely, if not entirely, manually controlled. In short, such aircraft are not equipped with a “fly by wire” configuration susceptible to easy automation of the level of engine power output (such as the case with respect to the above mentioned large turbine aircraft, or perhaps in the case of new military unmanned aerial vehicles). Engine performance in general aviation aircraft is set by manual adjustment of the separate throttle, mixture, and propeller controls. So, even if sophisticated flight management systems are available in such aircraft, as is the case in most newly produced aircraft, there remains a problem with respect to control of engine operation in a manner that would enable an emergency descent to be accomplished quickly and safely.
Consequently, there still remains an as yet unmet need in general aviation for an improved general aviation aircraft flight management system design, and for a method of operation of turbocharged piston engines, that would enable the flight management system to take full advantage of the existing mechanical design components with respect to engine operation, and with modest modifications, provide additional software control to enable the aircraft systems and avionics equipment to provide for timely and safe controlled descent in the case of incapacitation of the aircraft pilot(s).
Moreover, it would be advantageous to accomplish such goals while providing such improvements as upgrades to older avionics systems in existing aircraft, and as modifications to existing engines or to current production designs, in order to minimize the extent, complexity, and cost of any required recertification efforts with respect to such improved general aviation aircraft.